Oh big edit, I just realized my Vamo was set to AVG mode from the factory and not RMS mode. So much for my so called sweet spot I have been using at 3.4v. Newby move, even being technologically inclined I forgot to check that lol. Even in technical troubleshooting I always have this problem of skipping over the easiest solution to the problem. Here may be your solution, make sure you are in RMS mode and not AVG mode. Hold down the ' - ' or ' + ' button for 10-15 seconds until you see N01 or N02. When it displays N02 you are in RMS mode and you are good to go to higher voltages

. AVG mode is basically like blind firing, you may be at lower voltage/wattage and it is really vaping at a higher voltage/wattage. RMS is more accurate so try that out.
Another edit: once changed to RMS mode (N02) I am up at 4.2 and still working on voltage to hit that sweet spot. I bet this is your exact problem. Just hold down the minus (-) button for 10-15 seconds and you will see N02 mode and you are good to go! Enjoy!